;(function (doc, win, uisize, prem) {
  //1.html元素
  let html = doc.documentElement
  //2.声明事件名称
  let resizeEvent = 'orientationchange' in win ? 'orientationchange' : 'resize'
  //3.声明计算html的fontsize的函数
  function recalculate() {
    let clientWidth = html.clientWidth
    if (!clientWidth) {
      return
    }
    let rate = clientWidth / uisize
    html.style.fontSize = rate * prem + 'px'
  }
  //4.监听窗口缩放事件
  win.addEventListener(resizeEvent, recalculate, false)
  //5.监听文档加载结束事件
  doc.addEventListener('DOMContentLoaded', recalculate, false)
})(document, window, 750, 100)
